Electromechanical brake and method of operating the same

ABSTRACT

Disclosed is an electromechanical brake and a method of operating the same. In accordance with an aspect of the disclosure a electromechanical brake includes a piston configured to advance and retreat to press a brake pad; a power transmission unit configured to receive a driving force from an actuator to convert a rotational motion into a linear motion, and provide the converted driving force to the piston; and a position adjustment unit configured to adjust a relative position of the piston with respect to the power transmission unit; wherein the power transmission unit includes a spindle rotating by receiving the driving force from the actuator, and a nut connected to the spindle and moving forward or backward an inside of the piston by rotation of the spindle in a first direction or a second direction to advance and retreat the piston, wherein the position adjustment unit includes a first screw thread formed on an outer circumferential surface of the nut, a second screw thread formed on an inner circumferential surface of the piston and meshing with the first screw thread, and an adjuster provided between the spindle and the nut and configured to rotate the nut in the first direction or the second direction by rotation of the spindle to advance and retreat the relative position of the piston.

TECHNICAL FIELD

The present disclosure relates to an electromechanical brake and amethod of operating the same, and more particularly, to anelectromechanical disc brake for realizing braking of a vehicle using arotational driving force of a motor and a method of operating the same.

BACKGROUND ART

Generally, a vehicle is essentially equipped with a brake system forperforming braking, and various types of brake systems have beenproposed for a safety of a driver and a passenger.

Conventional brake systems mainly use a method of supplying hydraulicpressure required for braking to a wheel cylinder using a mechanicallyconnected booster when a driver depresses a brake pedal. However,nowadays, as a next-generation brake system, development of anelectromechanical brake system that receives a driver’s intention tobrake as an electric signal and operates an electric device such as amotor based on the electric signal to provide braking power to a vehiclehas been ongoing.

Such electromechanical brake systems convert rotational force of a motorinto linear motion through a motor and a speed reducer to provide aclamping pressure to a brake disc, thereby performing a service brakeand a parking brake of the vehicle.

On the other hand, brake pads that directly contact and press a brakedisc of a vehicle are gradually abraded according to the repeatedbraking operation of a vehicle. To maintain braking performance of avehicle despite wear of brake pads, implement of compensating for thewear of brake pads is required. However, in this case, applicability ofa vehicle decreases due to an increase in a size or axial length of abrake system.

DISCLOSURE Technical Problem

An aspect of the disclosure is to provide an electromechanical brakesystem capable of maintaining and improving braking performance of avehicle despite wear of brake pads, and a method of operating the same.

Another aspect of the disclosure is to provide an electromechanicalbrake system capable of stably braking a vehicle in various operatingconditions of the vehicle, and a method of operating the same.

Another aspect of the disclosure is to provide an electromechanicalbrake system capable of reducing size and weight to improveapplicability of a vehicle and to promote space utilization of avehicle, and a method of operating the same.

Another aspect of the disclosure is to provide an electromechanicalbrake system capable of easily compensating for wear of brake pads witha simple structure, and a method of operating the same.

Another aspect of the disclosure is to provide an electromechanicalbrake system capable of improving braking performance by reducing a dragphenomenon and suppressing braking noise and vibration, and a method ofoperating the same.

Technical Solution

In accordance with an aspect of the present disclosure, anelectromechanical brake includes a piston configured to advance andretreat to press a brake pad; a power transmission unit configured toreceive a driving force from an actuator to convert a rotational motioninto a linear motion, and provide the converted driving force to thepiston; and a position adjustment unit configured to adjust a relativeposition of the piston with respect to the power transmission unit;wherein the power transmission unit includes a spindle rotating byreceiving the driving force from the actuator, and a nut connected tothe spindle and moving forward or backward an inside of the piston byrotation of the spindle in a first direction or a second direction toadvance and retreat the piston, wherein the position adjustment unitincludes a first screw thread formed on an outer circumferential surfaceof the nut, a second screw thread formed on an inner circumferentialsurface of the piston and meshing with the first screw thread, and anadjuster provided between the spindle and the nut and configured torotate the nut in the first direction or the second direction byrotation of the spindle to advance and retreat the relative position ofthe piston.

The adjuster may include a flange extending radially on an outercircumferential surface of the spindle, a first protrusion protrudingfrom the flange, and a second protrusion protruding from the nut andconfigured to induce and generate the first direction rotation of thenut by being caught by the first protrusion when the spindle rotates inthe first direction, thereby advancing the relative position of thepiston.

A first angle between the first projection and the second projection ina braking release state of a vehicle may be provided to be greater thana second angle at which the first protrusion rotates from the brakingrelease state to a braking state of the vehicle.

The adjuster may further include a third protrusion protruding from theflange, wherein the second protrusion is configured to induce the seconddirection rotation of the nut by being caught by the third protrusionwhen the spindle rotates in the second direction, thereby retreating therelative position of the piston.

A third angle between the second protrusion and the third protrusion ina braking state of the vehicle may be provided to be greater than afourth angle at which the third protrusion rotates from the brakingstate to the braking release state of the vehicle.

The nut may include an internal thread formed on an innercircumferential surface thereof, the spindle may include a first end onone side of which an external thread meshing with the internal thread isformed on the outer circumferential surface thereof, a second end on theother side connected to the actuator, and a central portion disposedbetween the first end and the second end, and the flange may be fixedlyinstalled on an outer circumferential surface of the central portion.

The first protrusion and the third protrusion may be formed to protrudeto be spaced apart from each other on a front surface of the flangeopposite to the nut, and the second protrusion may be formed to protrudefrom an rear surface of the nut opposite to the front surface of theflange.

The electromechanical brake may further include an electronic controlunit configured to control operation of the actuator, and a detectionunit configured to detect an engaging force between the brake pad andthe disk rotating together with a wheel.

In accordance with another aspect of the present disclosure, a method ofoperating the electromechanical brake includes, in response to that theengaging force between the disc and the brake pad detected by thedetection unit in a braking state of the vehicle is less than apredetermined value, determining, by the electronic control unit, thatwear of the brake pad presents, and entering, by the electronic controlunit, a first mode for advancing the relative position of the piston.

The method may further include, in response to that the engaging forcebetween the disc and the brake pad detected by the detection unit in abraking release state of the vehicle is greater than a predeterminedvalue, determining, by the electronic control unit, that the a dragpresents, and entering, by the electronic control unit, a second modefor retreating the relative position of the piston.

The method may further include, in the first mode, by the electroniccontrol unit, controlling the operation of the actuator to rotate thespindle in a first direction from a braking release state of the vehicleto a braking state of the vehicle, generating an additional firstdirection rotation of the spindle to cause the first projection to berotated while contacting with the second projection, thereby inducingthe first direction rotation of the nut, and advancing the relativeposition of the piston with respect to the nut by the first directionrotation of the nut.

The method may further include, after the first mode, returning, by theelectronic control unit, the spindle or the first protrusion to itsoriginal position of the braking release state of the vehicle.

The method may further include, in the second mode, by the electroniccontrol unit, controlling the operation of the actuator to rotate thespindle in a second direction from a braking state of the vehicle to abraking release state of the vehicle, generating an additional seconddirection rotation of the spindle to cause the third projection to berotated while contacting with the second projection, thereby inducingthe second direction rotation of the nut, and retreating the relativeposition of the piston with respect to the nut by the second directionrotation of the nut.

Advantageous Effects

An embodiment of disclosure may provide an electromechanical brakesystem capable of maintaining and improving braking performance of avehicle despite wear of brake pads, and a method of operating the same.

Further, an embodiment of disclosure may provide an electromechanicalbrake system capable of stably braking a vehicle in various operatingconditions of the vehicle, and a method of operating the same.

Further, an embodiment of disclosure may provide an electromechanicalbrake system capable of reducing size and weight to improveapplicability of a vehicle and to promote space utilization of avehicle, and a method of operating the same.

Further, an embodiment of disclosure may provide an electromechanicalbrake system capable of easily compensating for wear of brake pads witha simple structure, and a method of operating the same.

Further, an embodiment of disclosure may provide an electromechanicalbrake system capable of improving braking performance by reducing a dragphenomenon and suppressing braking noise and vibration, and a method ofoperating the same.

DESCRIPTION OF DRAWINGS

FIG. 1 is a lateral cross-sectional view illustrating anelectromechanical brake according to an embodiment of the disclosure.

FIG. 2 is a lateral cross-sectional view illustrating an enlarged mainpart of an electromechanical brake according to an embodiment of thedisclosure.

FIG. 3 is an exploded perspective view illustrating the main part of theelectromechanical brake according to the embodiment of the disclosure.

FIG. 4 is a cross-sectional view taken along A-A′ direction of FIG. 2 ,illustrating positions of first, second, and third projections in abefore braking state of a vehicle or a braking release state of avehicle.

FIG. 5 is a lateral cross-sectional view illustrating an operation ofthe electromechanical brake according to an embodiment of the disclosurein a braking state of a vehicle.

FIG. 6 is a cross-sectional view taken along B-B′ direction of FIG. 5 ,illustrating positions of the first, second, and third projections inthe braking state of the vehicle.

FIG. 7 is a lateral cross-sectional view illustrating an operation ofthe electromechanical brake according to an embodiment of the disclosurein a first mode state for compensating for wear of brake pads.

FIG. 8 is a cross-sectional view taken along C-C′ direction of FIG. 7 ,illustrating positions of the first, second, and third protrusions inthe first mode state.

FIG. 9 is a lateral cross-sectional view illustrating an operation ofthe electromechanical brake according to an embodiment of the disclosurein the braking release state of the vehicle after the first mode.

FIG. 10 is a cross-sectional view taken along D-D′ direction of FIG. 9 ,illustrating positions of the first, second, and third projectionsdisclosure in the braking release state of the vehicle after the firstmode.

FIG. 11 is a lateral cross-sectional view illustrating an operation ofthe electromechanical brake according to an embodiment of the disclosurein a second mode for reducing drag.

FIG. 12 is a cross-sectional view taken along E-E′ direction of FIG. 11, illustrating positions of the first, second, and third protrusions inthe second mode.

MODES OF THE INVENTION

Hereinafter, the embodiments of the disclosure will be described indetail with reference to accompanying drawings. It should be understoodthat the terms used in the specification and the appended claims shouldnot be construed as limited to general and dictionary meanings, butinterpreted based on the meanings and concepts corresponding totechnical aspects of the disclosure on the basis of the principle thatthe inventor is allowed to define terms appropriately for the bestexplanation. Therefore, the description proposed herein is just apreferable example for the purpose of illustrations only, not intendedto limit the scope of the disclosure, so it should be understood thatother equivalents and modifications could be made thereto withoutdeparting from the spirit and scope of the disclosure.

FIG. 1 is a lateral cross-sectional view illustrating anelectromechanical brake 100 according to an embodiment of thedisclosure.

Referring to FIG. 1 , an electromechanical brake 100 according to anembodiment of the disclosure may include a carrier (not shown) on whicha pair of pad plates 11 and 12 are installed to press a disk (not shown)rotating together with a wheel of a vehicle, a caliper housing 20 thatis slidably installed on the carrier to operate the pair of pad plates11 and 12, a piston 110 that is installed to move forward and backwardinside the caliper housing 20, an actuator (not shown) that generatesand provides a driving force for moving the piston 110, a powertransmission unit 120 that realizes forward and backward movement of thepiston 110 in an axial direction by converting rotational driving forceprovided from the actuator into linear motion to transmit to the piston110, a position adjustment unit 130 that compensates for wear of brakepads 10 or reducing drag phenomenon by adjusting a relative position ofthe piston 110 with respect to the power transmission unit 120, adetection unit 140 that detects adhesion force between the disk 10 andthe brake pads 10 or engaging force of the brake pads 10, and anelectronic control unit (not shown, ECU) that controls an operation ofthe actuator based on information provided from the detection unit 140.

The pair of pad plates 11 and 12 is provided with the brake pad 10attached to an inner surface thereof, respectively. The pair of padplates have the inner pad plate 11 disposed so that an outer surfacethereof is in contact with a front surface (a left surface based on FIG.1 ) of the piston 110, and the outer pad plate 12 disposed so that anouter surface thereof is in contact with a finger part 22 of the caliperhousing 20. The pair of pad plates 11 and 12 is slidably installed onthe carrier.

The caliper housing 20 includes the finger part 22 for operating theouter pad plate 12 and a cylinder part 21 in which the piston 110 isinstalled, and is slidably fastened to the carrier. When the vehicle isa braking operation, the caliper housing 20 slides from the carrier by areaction force caused by the movement of the piston 110 and approachesthe disk, and in turn the outer pad plate 12 by the finger part 22approaches the disk side, thereby pressing the disk.

FIGS. 2 and 3 are lateral cross-sectional and exploded perspective viewsillustrating enlarged main part of the electromechanical brake 100according to an embodiment of the embodiment. Referring to FIGS. 1 to 3, the piston 110 may be provided in a cup shape in which a rear sidethereof (a right side based on FIGS. 1 and 2 ) is opened, and isslidably inserted inside the cylinder part 21. Furthermore, the piston110 may receive power through the actuator and the power transmissionunit 120 to be described later and press the inner pad plate 11 againstthe disk side. A second screw thread 132 that meshes with a first screwthread 131 formed on an outer circumferential surface of a nut 125 to bedescribed later may be formed on an inner circumferential surface of thepiston 110. Furthermore, as will be described later, when the nut 125 isrotated by the position adjustment unit 130, an anti-rotation portion(not shown) may be provided in the piston 110 so that the piston 110 mayperform a linear motion toward the pad plate side without rotatingtogether with the nut 125. An operation of adjusting a relative positionof the piston 110 with respect to a spindle 121 or the nut 125 by theposition adjustment unit 130 will be described later with reference toFIGS. 4 to 12 .

The power transmission unit 120 may include the spindle 121 that rotatesby receiving a driving force from the actuator (not shown), the nut 125that is disposed inside the piston 110 and is screw-coupled to thespindle 121 to move forward together with the piston 110 by a firstdirection rotation of the spindle 121 or to move backward together withthe piston 110 by a second direction rotation of the spindle 121, and aplurality of balls (not shown) interposed between the spindle 121 andthe nut 125. The power transmission unit 120 may be provided as aball-screw type transmission device that converts a rotational motion ofthe spindle 121 into a linear motion.

Here, the first direction rotation of the spindle 121 refers to arotation direction in which the nut 125 is advanced by the rotation ofthe spindle 121, and the second direction rotation of the spindle 121refers to a rotation direction in which the nut 125 is retracted by therotation of the spindle 121 as rotation in a direction opposite to thefirst direction.

The spindle 121 includes a first end 121 a on one side of which anexternal thread 122 is formed on an outer circumferential surfacethereof, a second end 121 c on the other side connected to the actuatorto receive the driving force, and a central portion 121 b disposedbetween the first end 121 a and the second end 121 c to which a flange136 to be described later is fixed. The first end 121 a of the spindle121 may be inserted into the nut 125, and a bearing 150 that promotessmooth rotation of the flange 136 to be described later and thedetection unit 140 for sensing a load applied to the spindle 121 andmeasuring an engaging force between the disc and the brake pads 10 maybe disposed on the second end 121 c.

The nut 125 may be formed in a hollow cylindrical shape so that thefirst end 121 a of the spindle 121 is inserted therein, and an internalthread 126 that meshes with the external thread 122 of the spindle 121through balls (not shown) may be formed on an inner circumferentialsurface of the nut. As such, the ball-screw type power transmissiondevice is a well-known technology that is already widely applied, so adetailed description of operation thereof will be omitted.

Meanwhile, the first screw thread 131 that meshes with the second screwthread 132 formed on the inner circumferential surface of the piston 110may be formed on the outer circumferential surface of the nut 125, and adetailed description thereof will be described later.

The actuator (not shown) may include a motor and a reducer having aplurality of reduction gears, and may receive power from a power supplydisposed in the vehicle to generate and provide a driving force. Theactuator may transmit the driving force generated by being connected tothe second end 121 c of the spindle 121 to a rotational motion of thespindle 121. The actuator may be installed on the outside of the caliperhousing 20, and the reducer may be provided to the spindle 121 bydecelerating power of the motor by applying devices with variousstructures such as a planetary gear assembly or a worm structure.

The position adjustment unit 130, by adjusting the relative position ofthe piston 110 with respect to the power transmission unit 120, mayadvance the relative position of the piston 110 so as to compensate forwear of the brake pads 10, or retreat the relative position of thepiston 110 in order to reduce drag phenomenon.

The position adjustment unit 130 may include the first screw thread 131formed on an outer circumferential surface of the nut 125, the secondscrew thread 132 that is formed on the inner circumferential surface ofthe piston 110 and meshes with the first screw thread 131, and anadjuster 135 provided between the spindle 121 and the nut 125. Theadjuster 135 rotates the nut 125 in the first direction by the rotationof the spindle 121 to advance the relative position of the piston 110 orrotates the nut 125 in the second direction opposite to the firstdirection to retreat the relative position of the piston 110.

Here, the first direction rotation of the nut 125 described below is thesame rotational direction as the first direction rotation of the spindle121 described above, and refers to a rotational direction in which thepiston 110 is advanced by the rotation of the nut 125. Furthermore, thesecond direction rotation of the nut 125, which is a rotation in theopposite direction to the first direction, is the same rotationaldirection as the second direction rotation of the spindle 121 describedabove, and refers to a rotational direction in which the piston 110 isreversed by the rotation of the nut 125.

The first screw thread 131 may be formed on the outer circumferentialsurface of the nut 125, the second screw thread 132 may be formed on theinner circumferential surface of the piston 110, and the first andsecond screw threads 131 and 132 are provided by meshing with eachother. As such, because the nut 125 and the piston 110 are screw-coupledto each other, the nut 125 and the piston 110, which are linearly movedtogether, may move forward together during braking of a general vehicle,or may move backward together during braking release of a vehicle. Atthe same time, because the piston 110 and the nut 125 may rotaterelative to each other, the piston 110 according to the rotation of thenut 125 in the first direction may move forward relatively with respectto the nut 125 or the spindle 121, and the piston 110 according to therotation of the nut 125 in the second direction, which is opposite tothe first direction, may move backward relatively with respect to thenut 125 or the spindle 121.

The adjuster 135 may cause the rotation of the nut 125 to advance orretreat the relative position of the piston 110 with respect to the nut125. The adjuster 135 may include a flange 136 that is fixed to thecentral portion 121 b of the spindle 121 and is formed to expand in aradial direction thereof, a first protrusion 137 protruding from a frontsurface (a left side based on FIG. 2 ) of the flange 136, a secondprotrusion 138 that is protruded from an rear surface (a right sidebased on FIG. 2 ) of the nut 125 and is caught by the first protrusion137 to induce and generate the first direction rotation of the nut 125when the spindle 121 rotates in the first direction, and a thirdprotrusion 139 that is protruded from front surface (a left side basedon FIG. 2 ) of the flange 136 and is caught by the second protrusion 138to induce and generate the second direction rotation of the nut 125 whenthe spindle 121 rotates in the second direction.

The flange 136 is radially extended to the central portion 121 b of thespindle 121, and is fixed to the spindle 121 to rotate integrally withthe spindle 121. The first and third protrusions 137 and 139, which willbe described later, may be formed to protrude from the front surface(the left side based on FIG. 2 ) of the flange 136 by being spaced apartfrom each other at a predetermined angle. A bearing 150 that promotessmooth rotation of the flange 136 and prevents abrasion between theflange 136 and surrounding components may be provided on the rearsurface (the right side based on FIG. 2 ).

The first and third protrusions 137 and 139 are formed to protrude fromthe front surface (the left side based on FIG. 2 ) of the flange 136opposite to the nut 125, and may rotate about the spindle 121 as an axistogether with the flange 136 when the spindle 121 rotates. The secondprotrusion 138 is formed to protrude from the rear surface (the rightside based on FIG. 2 ) of the nut 125 opposite to the flange 136, andmay be caught by the first protrusion 137 or the third protrusion 139 toinduce the rotation of the nut 125.

FIG. 4 is a cross-sectional view taken along A-A′ direction of FIG. 2 ,and shows positions of the first to third protrusions 137, 138, and 139in a before braking state or in a braking release state of the vehicle.Referring to FIG. 4 , the first and third protrusions 137 and 139provided on the front surface of the flange 136 are formed to protrudeat an angle spaced apart from each other, and the second protrusion 138provided on the rear surface of the nut 125 may be disposedtherebetween.

More specifically, an angle between the first protrusion 137 on thefront side of the flange 136 and the second protrusion 138 on the rearside of the nut 125 (hereinafter referred to as a first angle) in abefore braking state or in a braking release state of the vehicle isprovided to be greater than an rotation angle of the first protrusion137 (see FIG. 6 , hereinafter referred to as a second angle) from thebraking release state of the vehicle to the braking state of thevehicle. When the second angle ② is provided larger than the first angle①, the second protrusion 138 is caught by the first protrusion 137 evenwhen a general vehicle is braked to cause the nut 125 to be rotated inthe first direction. Accordingly, the relative position of the piston110 with respect to the nut 125 or the spindle 121 advances to increaserapidly an engaging force between the piston 110 and the pad plates, sothat a braking force of the vehicle is greater than a driver’s brakingdemand, and further, driving stability and fuel efficiency of thevehicle may be deteriorated due to the occurrence of a drag phenomenon.Accordingly, by providing the first angle ① larger than the second angle②, it is possible to prevent the first protrusion 137 and the secondprotrusion 138 from contacting each other during general vehiclebraking, and thus, the relative position of the piston 110 with respectto the nut 125 or the spindle 121 may be constantly maintained topromote braking operability and driving stability of a driver.

Furthermore, in the braking state of the vehicle, an angle between thesecond protrusion 138 on the rear side of the nut 125 and the thirdprotrusion 139 on the front side of the flange 136 (see FIG. 6 ,hereinafter referred to as a third angle) is provided to be greater thanan rotation angle of the third protrusion 139 (see FIGS. 4 and 6 ,hereinafter referred to as a fourth angle) from the braking state of thevehicle to the braking release state of the vehicle. When the fourthangle ④ is greater than the third angle ③, the second protrusion 138 iscaught by the third protrusion 139 even when braking of a generalvehicle is released to cause the nut 125 to be rotated in the seconddirection. Accordingly, the relative position of the piston 110 withrespect to the nut 125 or the spindle 121 is retreated to reduce theengaging force between the piston 110 and the pad plates, so that thebraking force of the vehicle acts smaller than the driver’s brakingdemand, leading to a safety accident. Accordingly, by providing thethird angle ③ larger than the fourth angle ④, it is possible to preventthe second protrusion 138 and the third protrusion 139 from contactingeach other when braking of a general vehicle is released, and thus, therelative position of the piston 110 with respect to the nut 125 or thespindle 121 may be constantly maintained to promote braking operabilityand driving stability of the driver.

The detection unit 140 is provided to detect adhesion force or engagingforce between the disc and the brake pads 10. The detection unit 140 maybe provided as a force sensor that detects the load of the spindle 121or the actuator to measure the engaging force between the disc and thebrake pads 10, but is not limited thereto. The detection unit 140 maytransmit information on the detected engaging force of the brake pad 10to the ECU, and the ECU may determine wear or drag of the brake pads 10based on the information on the engaging force detected by the detectionunit 140.

Hereinafter, an operation method of the electromechanical brake 100system according to an embodiment of the disclosure will be described.

FIG. 5 is a lateral cross-sectional view illustrating the operation ofthe electromechanical brake 100 according to an embodiment of thedisclosure in the braking state of the vehicle, and FIG. 6 is across-sectional view taken along B-B′ direction of FIG. 5 , showing thepositions of the second protrusion 138 and the third protrusion 139.

Referring to FIGS. 2 and 4 to 6 , during general braking that does notenter a first mode or a second mode to be described later, such as aservice brake or parking brake of the vehicle, the electromechanicalbrake system may operate from the braking release state as shown inFIGS. 2 and 4 to the braking state as shown in FIGS. 5 and 6 .

More specifically, when a driver applies an effort force to a brakepedal (not shown) to brake the vehicle, a pedal displacement sensor (notshown) detects a driver’s intention to brake as an electrical signal andtransmits the detected electric signal to the ECU. The ECU, based on theelectrical signal, may control the operation of the actuator so that thedisc and the brake pad 10 come into close contact to each other, therebyimplementing braking of the vehicle.

When the vehicle is braked, the spindle 121 rotates in the firstdirection by the operation of the actuator, and in turn the nut 125advances according to the rotation of the spindle 121 in the firstdirection, so that the piston 110 also advances toward the pad plate. Asthe brake pad 10 mounted on the pad plate approaches and closely adheresto the disc, the engaging force is generated, thereby causing thevehicle to be braked.

At this time, the first protrusion 137 provided on the flange 136 of thespindle 121 rotates by the second angle from the braking release stateof the vehicle to the braking state of the vehicle according to therotation of the spindle 121 in the first direction. However, because thefirst angle ① between the first protrusion 137 of the flange 136 and thesecond protrusion 138 of the nut 125 is provided larger than the secondangle in the braking release state of the vehicle, the first protrusion137 of the flange 136 and the second protrusion 138 of the nut 125 donot contact each other in the general braking situation. Accordingly,the relative position of the piston 110 with respect to the nut 125 orthe spindle 121 may be constantly maintained.

When braking of the vehicle is released, the electromechanical brakesystem may operate from the braking state as shown in FIGS. 5 and 6 tothe braking release state as shown in FIGS. 2 and 4 . More specifically,the spindle 121 rotates in the second direction by the operation of theactuator, and in turn the nut 125 retreats according to the rotation ofthe spindle 121 in the second direction, so that the piston 110 is alsospaced apart from and retreated from the pad plates 11 and 12. As thebrake pad 10 mounted on the pad plates 11 and 12 is spaced apart fromthe disk, thereby releasing braking of the vehicle. The first protrusion137 provided on the flange 136 of the spindle 121 returns to itsoriginal position according to the rotation of the spindle 121 in thesecond direction.

Hereinafter, the first mode in which the electromechanical brake 100according to an embodiment of the disclosure compensates for wear of thebrake pad 10 will be described so that braking performance of thevehicle may be maintained despite wear of the brake pad 10.

In response to that the adhesion force or engaging force between thedisc and the brake pad 10 measured by the sensor 140 in the brakingstate of the vehicle is less than a predetermined normal range value,the ECU determines that wear of the brake pad 10 presents and may enterthe first mode for compensating it.

FIG. 7 is a lateral cross-sectional view illustrating an operation ofthe electromechanical brake 100 according to an embodiment of thedisclosure in the first mode state for compensating for wear of thebrake pad 10, and FIG. 8 is a cross-sectional view taken along C-C′direction of FIG. 7 , showing the positions of the first, second, andthird protrusions 137, 138, and 139 in the first mode state.

Referring to FIGS. 7 and 8 , the ECU rotates the spindle 121 in thefirst direction by controlling the operation of the actuator so as toenter the first mode. At this time, the ECU generates an additionalfirst direction rotation (exceeding the first angle in FIG. 4 ) that ismore than the first direction rotation (see the second angles of FIGS. 5and 6 ) of the spindle 121 for the general braking state. As a result,the first protrusion 137 provided on the flange 136 of the spindle 121is rotated while contacting with the second protrusion 138 provided onthe nut 125. Because the second protrusion 138 is caught by the firstprotrusion 137 to rotate together in the first direction, the nut 125also rotate in the first direction. The relative position of the piston110 with respect to the nut 125 may advance by the first directionrotation of the nut 125, thereby compensating for wear of the brake pad10.

After completion of the first mode for compensating for wear of thebrake pad 10, the electromechanical brake 100 according to an embodimentof the disclosure returns to the braking release state or before brakingstate of the vehicle.

FIG. 9 is a lateral cross-sectional view illustrating an operation ofthe electromechanical brake 100 according to an embodiment of thedisclosure in the braking release state of the vehicle after the firstmode, and FIG. 10 is a cross-sectional view taken along D-D′ directionof FIG. 9 , showing the positions of the first, second, and thirdprotrusions 137, 138, and 139 are shown in the braking release state ofthe vehicle after the first mode.

Referring to FIGS. 9 and 10 , after compensating for wear of the brakepad 10 through the first mode, the ECU controls the operation of theactuator to generate the second direction rotation of the spindle 121.More specifically, as shown in FIGS. 2 and 4 , the actuator rotates thespindle 121 in the second direction to return the braking release stateor the before braking state of the vehicle. As described above, althoughthe additional first direction rotation of the spindle 121 occurs in thefirst mode, the ECU rotates the spindle 121 in the second direction byan amount corresponding to an amount of an additional rotation generatedin the first mode, so that the spindle 121 and the nut 125 may return totheir original positions.

As the spindle 121 returned to its original position after performingthe first mode rotates by the second angle when the vehicle is brakedagain, the braking operation is performed in a state that the relativeposition of the piston 110 with respect to the spindle 121 or the nut125 is compensated for wear of the brake pad 10, thereby performingstably braking of the vehicle.

Hereinafter, an operation in which the electromechanical brake 100according to an embodiment of the disclosure performs the second mode soas to reduce a drag phenomenon in which the piston 110 does not quicklyreturn to its original position after the braking operation of thevehicle will be described.

In response to that the adhesion force or engaging force between thedisc and the brake pad 10 measured by the sensor 140 in the brakingrelease state of the vehicle is greater than a predetermined normalrange value, the ECU determines that the drag phenomenon presents inwhich the piston 110 does not return to its original position, and mayenter the second mode.

FIG. 11 is a lateral cross-sectional view illustrating an operation ofthe electromechanical brake 100 according to an embodiment of thedisclosure in the second mode state for reducing drag, and FIG. 12 is across-sectional view taken along E-E′ direction of FIG. 11 , showing thepositions of the first, second, and third protrusions 137, 138, and 139in the second mode state.

Referring to FIGS. 11 and 12 , the ECU rotates the spindle 121 in thesecond direction by controlling the operation of the actuator so as toenter the second mode. At this time, the ECU generates an additionalsecond direction rotation (exceeding the third angle in FIG. 4 ) that ismore than the second direction rotation of the spindle 121 for thegeneral braking release state, so that the third protrusion 139 providedon the flange 136 of the spindle 121 is caught by the second protrusion138 provided on the nut 125. As the second protrusion 138 is caught bythe third protrusion 139 to rotate together in the second direction, thenut 125 also rotate in the second direction. The relative position ofthe piston 110 with respect to the nut 125 may be retreated by thesecond direction rotation of the nut 125, so that the piston 110 isspaced apart from the pad plate to reduce the drag.

1. An electromechanical brake, comprising: a piston configured to advance and retreat to press a brake pad; a power transmission unit configured to receive a driving force from an actuator to convert a rotational motion into a linear motion, and provide the converted driving force to the piston; and a position adjustment unit configured to adjust a relative position of the piston with respect to the power transmission unit; wherein the power transmission unit comprises: a spindle rotating by receiving the driving force from the actuator, and a nut connected to the spindle and moving forward or backward an inside of the piston by rotation of the spindle in a first direction or a second direction to advance and retreat the piston, wherein the position adjustment unit comprises: a first screw thread formed on an outer circumferential surface of the nut, a second screw thread formed on an inner circumferential surface of the piston and meshing with the first screw thread, and an adjuster provided between the spindle and the nut and configured to rotate the nut in the first direction or the second direction by rotation of the spindle to advance and retreat the relative position of the piston.
 2. The electromechanical brake of claim 1, wherein the adjuster includes: a flange extending radially on an outer circumferential surface of the spindle, a first protrusion protruding from the flange, and a second protrusion protruding from the nut and configured to induce and generate the first direction rotation of the nut by being caught by the first protrusion when the spindle rotates in the first direction, thereby advancing the relative position of the piston.
 3. The electromechanical brake of claim 2, wherein a first angle between the first projection and the second projection in a braking release state of a vehicle is provided to be greater than a second angle at which the first protrusion rotates from the braking release state to a braking state of the vehicle.
 4. The electromechanical brake of claim 2, wherein the adjuster further includes a third protrusion protruding from the flange, wherein the second protrusion is configured to induce the second direction rotation of the nut by being caught by the third protrusion when the spindle rotates in the second direction, thereby retreating the relative position of the piston.
 5. The electromechanical brake of claim 4, wherein a third angle between the second protrusion and the third protrusion in a braking state of the vehicle is provided to be greater than a fourth angle at which the third protrusion rotates from the braking state to the braking release state of the vehicle.
 6. The electromechanical brake of claim 4, wherein the nut includes an internal thread formed on an inner circumferential surface thereof, the spindle includes a first end on one side of which an external thread meshing with the internal thread is formed on the outer circumferential surface thereof, a second end on the other side connected to the actuator, and a central portion disposed between the first end and the second end, and the flange is fixedly installed on an outer circumferential surface of the central portion.
 7. The electromechanical brake of claim 6, wherein the first protrusion and the third protrusion are formed to protrude to be spaced apart from each other on a front surface of the flange opposite to the nut, and the second protrusion is formed to protrude from an rear surface of the nut opposite to the front surface of the flange.
 8. The electromechanical brake of claim 4, further comprising an electronic control unit configured to control operation of the actuator; and a detection unit configured to detect an engaging force between the brake pad and the disk rotating together with a wheel.
 9. A method of operating the electromechanical brake according to claim 8, the method comprising: in response to that the engaging force between the disc and the brake pad detected by the detection unit in a braking state of the vehicle is less than a predetermined value, determining, by the electronic control unit, that wear of the brake pad presents, and entering, by the electronic control unit, a first mode for advancing the relative position of the piston.
 10. The method of claim 9, further comprising: in response to that the engaging force between the disc and the brake pad detected by the detection unit in a braking release state of the vehicle is greater than a predetermined value, determining, by the electronic control unit, that the a drag presents, and entering, by the electronic control unit, a second mode for retreating the relative position of the piston.
 11. The method of claim 9, further comprising: in the first mode, by the electronic control unit, controlling the operation of the actuator to rotate the spindle in a first direction from a braking release state of the vehicle to a braking state of the vehicle, generating an additional first direction rotation of the spindle to cause the first projection to be rotated while contacting with the second projection, thereby inducing the first direction rotation of the nut, and advancing the relative position of the piston with respect to the nut by the first direction rotation of the nut.
 12. The method of claim 11, further comprising: after the first mode, returning, by the electronic control unit, the spindle or the first protrusion to its original position of the braking release state of the vehicle.
 13. The method of claim 10, further comprising: in the second mode, by the electronic control unit, controlling the operation of the actuator to rotate the spindle in a second direction from a braking state of the vehicle to a braking release state of the vehicle, generating an additional second direction rotation of the spindle to cause the third projection to be rotated while contacting with the second projection, thereby inducing the second direction rotation of the nut, and retreating the relative position of the piston with respect to the nut by the second direction rotation of the nut. 